Effect of intermetallic compounds on the bonding state of kinetic sprayed Al deposit on Cu after heat-treatment

Post heat-treatment has generally been applied to products in the spray coating field as a method of improving mechanical properties. For kinetic spray process, the heat-treatment condition of dissimilar material pair (coating and substrate) should be controlled carefully, since brittle intermetallic compounds can be created at the interface. In this study, Al was kinetic sprayed onto a Cu substrate and was heat-treated under various heat-treatment conditions to investigate the effect of CuAl intermetallic compounds on bond strength. When adhesive bond strength was tested, fracture was induced at the lower interface of the CuAl2 layer in all heat-treated specimens. The bond strength was enhanced at relatively lower temperature heat-treatment (300 and 350 °C) assisted by diffusion bonding between the Al deposit and Cu substrate. However, the bond strength was weakened sharply after heat-treatment at 400 °C due to decreased interaction between the Cu substrate and the diffused Cu elements, which resulted from the formation of a CuAl2 layer on the side of Al deposit. The bond strength recovered at 450 and 500 °C, since intimate bonding was achieved between the CuAl2 layer and the lower layer (Cu4Al3 or CuAl), which was chemically grown between the CuAl2 and Cu9Al4 layers.